Aligning means for an injection molding device

ABSTRACT

Vertical injection-molding device with aligning means ( 15 ) for mutually aligning the mold parts ( 33, 34 ) which can be displaced with respect to one another. These aligning means comprise three plates ( 56 - 58 ) placed one on top of the other. The outermost plates ( 58, 56 ) are secured to a mold part ( 33 ) and to the frame of the injection-molding device on the displacement means arranged thereon. The intermediate plate ( 57 ) is secured to the end plates ( 56, 58 ) via ribs ( 16, 17; 59, 60 ) which extend in the radial direction with respect to the direction of displacement of the moveable mold part ( 33 ). These ribs ( 16, 17; 59, 60 ) are arranged crosswise, so that an adjustment movement of the outermost plates ( 56, 58 ) with respect to one another is possible.

The present invention relates to an injection-molding device.

The construction described above can be used both for injection-moldingdevices with the mold parts secured rigidly, in which case in practicecorrections are constantly required, and when using injection-moldingdevices which are less rigid and in which the mold sections, during moldclosure, seek one another out, thus providing a centering action. Inboth cases, the positioning of the mold sections with respect to amachine becomes less critical and may change and maintenance can becarried out more easily. After all, the mold sections are centered withrespect to one another while the mold is being closed. In the case ofless rigid constructions, the frame and associated structural parts canbe of considerably simpler design. As a result, production costs willdrop. Moreover, it is now easy to allow the device to operate, i.e.design it with a closure movement of the moveable mold section. This hasadvantages in certain cases when changing mold sections forinjection-molding of different products (centering with respect to theirreceiving part) and during removal of products after injection-molding.Unlike with horizontally acting injection-molding devices, centeringbetween the two mold parts is achieved by mutual displacement of thesaid mold parts with respect to the frame. Since the frame can be ofnon-rigid design, its construction can be relatively lightweight andcompact. However, this means that high demands are imposed on thealigning means which act between a mold part and the frame.

The non-rigid connection between the actuating means and the moveablemold section may comprise any connection which is known in the priorart. This connection merely has to be rigid in the direction of closure.A spherical bearing is mentioned by way of example. If appropriate, thismay be designed as a system with a ball both in the vicinity of the moldsection and at the actuating means, with a double socket positionedtherebetween. In this way, a double thrust bearing is formed, allowingtilting and slight movement in the horizontal plane (during a closuremovement) of the moveable mold section with negligible friction.

The object of the present invention is to provide a non-rigid connectionbetween one of the mold parts and the frame and/or the actuating meansfor opening and closing said mold part. This needs to be of simpledesign, in such a manner that there is no mutual displacement alongmetallic surfaces which is limited by friction, as is the case withthrust bearings.

This object is achieved with an injection-molding device comprising aframe which extends with a first mold part, which cannot be displacedalong an axis, on the top side or underside, and a second mold part,which can be displaced along an axis, on the underside or top side,displacement means, which are arranged between the frame and the secondmold part in order to displace the second mold part from and to thefirst mold part in order to carry out an injection-molding operation,aligning means being arranged between the frame and a mold part in orderto displace the free end face of the first mold part such that it bearsflat against the free end face of the second mold part, said aligningmeans comprising at least two ribs which lie in line with one anotherand extend perpendicularly and radially with respect to the axis in aplane, and which ribs are on the one hand connected to a mold part andon the other hand connected to the frame or the displacement means,which ribs end at a central opening. The use of ribs which function as ahinge results in a low-friction construction which can bear high loadsand with which it is possible for the relevant surfaces of two moldparts which are moving toward one another to be placed in precisely thecorrect position.

According to an advantageous embodiment, displacement in two directionswhich are perpendicular to one another is possible, and for this purposethere are two sets of ribs which extend perpendicular to one another,with an intermediate plate between them.

The cross section of the ribs halfway up them in a directionperpendicular to the axis of the injection-molding device may beconstant. However, according to an advantageous embodiment of theinvention, this is designed to converge toward the outer end of themold. This convergence is preferably tapered. The outer boundary of theribs is preferably a continuous line in order to avoid stresses as faras possible. More particularly, this line is part of a circularcylinder.

Designing the cross section of the ribs to converge toward the radialouter periphery results in the formation of a construction which can besubjected to relatively high loads and is not particularly rigid. If theribs were to have a constant cross section over their radial extent,they would be more rigid for the same load-bearing capacity.

The aligning means described above can be used in combination with anumber of columns which extend in the direction of displacement. Thesecolumns are arranged between the actuating means and the moveable part.The columns are rigid in the longitudinal direction, i.e. in thedirection of displacement (high compressive strength) and weak in thetransverse direction. The weakness can be implemented by arrangingrecesses, such as grooves, in the columns. As a result of a number ofcolumns being arranged next to and parallel to one another, displacementof the bottom connecting surface with respect to the top connectingsurface is possible, but the presence of the columns means that thismovement is purely parallel, i.e. a type of parallelogram structure isformed. It has been found that if a larger number of columns is used,the overall “weakness” of the structure, i.e. its ability to move in thedirection perpendicular to the direction of displacement, may increase.A number which is practical is four, but any other number may also beused.

The aligning means described above can be used in both a verticalinjection-molding device and a horizontal injection-molding device.

It should be understood that the invention can also be used exclusivelywith the aligning means described above.

The invention will be described in more detail below with reference toan exemplary embodiment of the invention which is depicted in thedrawing, in which:

FIG. 1 diagrammatically depicts a cross section through theinjection-molding device according to the present invention with theactuating means in the molding position;

FIG. 2 shows the centering means shown in FIG. 1 in more detail; and

FIG. 3 shows a partially cut-away view of a variant of the centeringmeans shown in FIG. 2.

In FIG. 1, the injection-molding device according to the invention isdenoted overall by 1. It comprises an upper frame 2, which is connected,for example by means of three or four columns 3, to the base plate 4 ina relatively “weak” way. In the design shown here, the injection-moldingdevice is arranged vertically, i.e. the mold sections move in thevertical direction with respect to one another.

The actuating means for the moveable mold section comprises a crankshaft5 which is driven in some way by a motor and control unit, not shown inmore detail. The crank of crankshaft 5 is connected to a drive rod 6which, in the vicinity of its free end, is provided with a pivot 9, towhich auxiliary rods 7 and 8 are pivotably secured. Auxiliary rod 7 isconnected to pivot 10 of piston 14, while auxiliary rod 8 engages onpivot 11 on the end of the plunger rod of ram 13. In the position of theplunger rod of ram 13 which is shown in FIG. 1, the mold cavity can becompletely closed, i.e. the mold sections can be moved completelytogether, by movement of crankshaft 5.

The moveable mold section 33 is connected, via a centering structure 15,to the piston 14 or other reciprocatingly driven part. This centeringstructure, which is used to ensure that the end face of mold section 33which faces the mold section 34 comes to lie parallel to the end face ofmold section 34 which faces mold section 33, comprises a plate 54 whichis connected, in a manner which is not illustrated in more detail, topiston 14 (FIG. 1). Plate 58 is used to support mold section 33.

A number of (in this case four) columns 55 with a high compressivestrength are arranged on plate 54. They are provided with recesses 61,62 which always extend in horizontal directions. As a result, each ofthese columns is relatively weak in the transverse direction (as seen inthe drawing). On the other side, these columns are connected to plate56. This design allows high compressive forces to be transmitted fromplate 54 to plate 56. Moreover, plate 56 can move laterally (as seen inthe drawing) with respect to plate 54 but in doing so will alwaysmaintain the same orientation, i.e. if plates 54 and 56 are originallyparallel, they will remain parallel in the event of any lateralmovement. The use of a large number of columns 55 makes it possible toprovide a relatively weak structure, making it possible to provide foradjustments of tenths of a millimeter.

If, in the starting position, there is an incorrect orientation withrespect to the angular position, it is possible to arrange a plate 57between plates 56 and 58. This plate 57 is always located at a distancefrom plates 56 and 58 and is connected thereto by a rib 59 or 60 whichextends radially with respect to central opening 19. As a result ofthese ribs being arranged perpendicular to one another, a tiltingmovement in two perpendicular directions (x-y) is possible. It will beunderstood that the alternative described above to a thrust bearing canbe used in combination with the thrust bearing or instead of it.Moreover, it is possible to use only the columns and/or only the twoplates 56, 57, 58 which can tilt with respect to one another.

In the embodiment shown here, the ribs 59, 60 arranged between theplates 56, 57 and 57, 58, respectively, have substantially the samedimension in the direction extending radially (with respect to thecenter axis 7). The plate 58 is provided with securing means for themold section 63.

FIG. 3 shows a variant of the design of the ribs. For the sake ofsimplicity, in this figure the plates are once again denoted by 56-58while the ribs bear reference numerals 16 and 17. They extend as far asopening 29.

It can be seen from this drawing that the cross-sectional plane of theribs 16, 17 as seen in FIG. 3 decreases in the radial direction from thecenter of the plates 56-58. There are (partially) circular-cylindricalopenings directly adjacent to the ribs.

Designing the ribs 16, 17 to taper in this way allows a uniform stressdistribution to be produced in the material of the ribs in the event ofdeformation, since in the event of displacement of the centeringstructure, a higher stress will occur in the center than in the vicinityof the periphery.

In this way, it is possible to obtain a much higher load-bearingcapacity than with the design shown in FIG. 2 with ribs of constantcross section, while using the same rigidity. It has been found that anincrease of 40% or more is possible.

To further increase the load-bearing capacity, the wall surface of theribs 16, 17 is preferably designed to be as smooth as possible, whichcan be achieved, for example, by honing. The diameter of thecircular-cylindrical opening adjoining the ribs should preferably besuch that it does not cause any notch effect.

Although the invention has been described above with reference to apreferred embodiment, it will be understood that numerous modificationscan be made to this embodiment without departing from the scope of thepresent application. For example, a vertical injection-molding device asshown in FIG. 1 may be designed in an entirely different way withoutdeparting from the scope of the appended claims.

1. Injection-molding device comprising a frame which extends with afirst mold part, which cannot be displaced along a vertical axis, on thetop side or underside, and a second mold part, which can be displacedalong a vertical axis, on the underside or top side, displacement means,which are arranged between the frame and the second mold part in orderto displace the second mold part from and to the first mold part inorder to carry out an injection-molding operation, aligning means beingarranged between the frame and a mold part in order to displace the freeend face of the first mold part such that it bears flat against the freeend face of the second mold part said aligning means comprising at leasttwo ribs which lie in line with one another and extend perpendicularlyand radially with respect to the vertical axis in a plane, and whichribs are on the one hand connected to a mold part and on the other handconnected to the frame or the displacement means, which ribs end at acentral opening.
 2. Injection-molding device as claimed in claim 1,comprising two sets of ribs which extend perpendicular to one anotherand are connected by an auxiliary plate.
 3. Injection-molding device asclaimed in claim 1, in which, as seen in cross section perpendicular tothe vertical axis taken halfway up the ribs, these ribs converge towardthe radially outer side.
 4. Injection-molding device as claimed in claim3, in which said ribs taper.
 5. Injection-molding device as claimed inclaim 1, in which, as seen in cross section perpendicular to the radialaxis of said ribs, the end boundary of said ribs is a continuous line.6. Injection-molding device as claimed in claim 5, in which the saidcontinuous line is a (part-) circle.
 7. Injection-molding device asclaimed in claim 5, in which the said ribs are delimited on either sideby a circular cylinder.
 8. Injection-molding device as claimed in claim1, comprising a vertical injection-molding device with a verticallyextending frame.
 9. (canceled)
 10. Mold part provided with aligningmeans being arranged on said mold part in order to displace the free endface of said mold part such that it is able to bear flat against thefree end face of a further mold part, said aligning means comprising atleast two ribs which lie in line with one another and extendperpendicularly and radially with respect to the vertical axis in aplane, and which ribs are connected on the one hand to said mold partand connectable on the other hand to a frame or displacement means,which ribs end at a central opening.